Preform conveying device

ABSTRACT

An object of this invention is to provide a preform conveying device of high production efficiency under the technical theme of aligning the plurality of preforms in single rows at high speed, while eliminating contact of individual preforms with other preforms and minimizing the chances of contact with device parts. 
     In a state in which a plurality of preforms are aligned vertically and laterally, preforms are received in a manner partitioned in vertical row units, and by putting a conveying line, formed along the direction of a vertical row of preforms, in an inclined orientation in which the downstream side is raised, positioning the upstream end of the conveying line above a preform receiving part, and moving the vertical row unit of preforms that is positioned along the conveying line in the vertical row direction at substantially the same speed as the conveying speed of the conveying line, the respective preforms of the vertical row unit are transferred in a state in which each is sandwiched by the conveying line and this is carried out successively for each vertical row unit to supply the plurality of preforms to a blow molding machine or other subsequent process side upon aligning them in single rows.

FIELD OF THE ART

This invention relates to a preform conveying device to be used inmanufacturing a molded container, such as a polyethylene terephthalateresin bottle, etc., and more specifically relates to a device, whichreceives, via an unloading device, preforms, molded by an injectionmolding machine having a plurality of preform molding cavities alignedvertically and laterally, aligns these preforms in single rows, andsupplies the preforms to a blow molding machine or subsequent processside.

BACKGROUND ART

Due to their performance, the applications of bottles and othercontainers formed of a biaxial drawing, blow-molded thermoplastic resin,such as polyethylene terephthalate (PET) resin, etc., are spreadinggreatly in a wide variety of fields, such as drink bottles, etc.Normally, such molded containers are manufactured by heating and meltinga plastic material by an injection molding machine to injection moldtest-tube-shaped preforms, conveying these preforms to a blow moldingmachine, and then guiding the preforms into the mold of the blow moldingmachine and performing the biaxial drawing blow molding processes ofvertical drawing by a draw pin and blowing of compressed air into thepreforms.

Various improvements have been attempted in the respective processes inorder to increase the production speed of the manufacture of suchcontainers. For example, for the processes of receiving preforms, whichhave been molded by an injection molding machine having a plurality ofpreform molding cavities aligned vertically and laterally, aligningthese preforms in single rows, and conveying them to the blow moldingmachine side, a preform conveying device (referred to hereinafter simplyas “conveying device”), such as shown in FIG. 6, has been used sincepriorly to improve the production speed.

The conveying device of FIG. 6 mainly comprises a conveyor part 32, anda preform feeder 33, having a function of aligning the orientation ofpreforms P in a fixed direction by the rotation action of a disk, andthis conveying device receives, by means of the conveyor part, aplurality of preforms P, which have been unloaded by an unloading device31 from an injection molding machine having a plurality of preformmolding cavities, and supplies the preforms to preform feeder 33 toalign the orientations of preforms P into single rows by using thecentrifugal force due to the rotation of the disk and convey them to theblow molding process side.

However, if the production speed is to be increased further, thepreforms must be handled in a state of higher temperature, and with theprior-art method illustrated in FIG. 6, the preforms can get damaged dueto collision or friction of preforms with themselves or with deviceparts.

Also, due to the high probability for preform surfaces coming in contactwith parts that make up the device, soiling of preform surfaces occursat a high frequency.

This invention has been made to solve the above-described problems ofthe prior art, and an object thereof is to provide a device thatreceives preforms that have been molded by an injection molding machinehaving a plurality of preform molding cavities aligned vertically andlaterally, aligns these preforms in single rows, and supplies them to ablow molding machine or other subsequent process side, wherein aconveying device of high production efficiency is provided under thetechnical theme of aligning the plurality of preforms in single rows athigh speed, while eliminating contact of individual preforms with otherpreforms and minimizing the chances of contact with device parts.

DISCLOSURE OF THE INVENTION

In order to achieve the above technical theme, a first aspect of variousexemplary embodiments of the preform conveying device of the inventionincludes a means, wherein provided is a device that receives, via anunloading device, preforms, which have been molded by an injectionmolding machine having a plurality of preform molding cavities alignedvertically and laterally, supplies these preforms to a subsequentprocess side upon alignment in single rows, the device comprising: apreform aligning part, having a slide table installed on a frame in amanner enabling sliding in a direction that is a single horizontaldirection and having, on the slide table, slide plates, each providedwith supporting parts that respectively hold individual preforms ininverted states at alignment positions corresponding to the alignment ofthe preforms in a single vertical row of the unloading device, the slideplates being at least the same in number as the number of vertical rowsof the unloading device and being aligned parallel to a horizontalX-direction, perpendicular to the Y-direction, at intervalscorresponding to the alignment of the vertical rows in a maimer enablingsliding individually in the X-direction; and a grip conveyor, havinggrips formed of a rubber-like soft material for holding the preforms ina sandwiching maimer and having, in a state in which a conveying lineformed thereby is aligned in direction in the X-direction and inclinedby the raising of a downstream part, an upstream end positioned abovethe preform alignment part; wherein each slide plate, upon beingsuccessively set by the sliding of the slide table in the Y-direction sothat its Y-direction position matches the Y-direction position of theconveying line formed by the grip conveyor, is slid in the X-directionat substantially the same speed as the conveying speed of the gripconveyor and moved below the grip conveyor as the individual preformsare transferred to the grip conveyor.

With the above arrangement according to exemplary embodiments, since theX-direction positions of the slide plates, which are the same in numberas the number of vertical rows of the plurality of preforms that arealigned vertically and laterally in the unloading device, are firstmatched with predetermined positions so that the supporting parts arealigned in a manner corresponding to the vertical and lateral alignmentof the unloading device, the preforms are transferred to the conveyordevice in the same alignment as that in the unloading device.

Then by the sliding of the slide table in the Y-direction, theY-direction position of the slide plate of the first row is matched withthe Y-direction position of the conveying line, formed by the gripconveyor, and is then slid in the X-direction at substantially the samespeed as the conveying speed of the grip conveyor to transfer theindividual preforms to the grip conveyor while moving below the gripconveyor.

Since in this process of transferring the preforms, the conveying speedsof the slide plate and the grip conveyor are substantially the same andthe grip conveyor is in a state in which its downstream part is raised,each preform is sandwiched from both sides at the body part by rubbergrips and is removed smoothly from the supporting part while being heldupwards to accomplish the transfer from the slide plate to the gripconveyor.

The preforms that have thus been transferred to the grip conveyor areconveyed to the blow molding process side.

Since preforms are handled by the above-described procedures, there isno collision or friction of preforms with each other and since thecontact of parts of the conveying device with the outer surfaces ofpreforms can be restricted to that of the gripping by the grips formedof a rubber-like, soft material, the problem of flawing of the preformsor the problem of the soiling of the outer surfaces of preforms will notoccur.

Also, since only the preforms are moved to the blow molding process orother subsequent process side and since movement to the subsequentprocess side, return to the conveying device, and realignment are thusmade unnecessary for the supporting parts, the conveying device can bemade simple in structure and handling.

A second aspect of exemplary embodiments includes the slide table beinginstalled in a manner enabling rising and lowering with respect to theframe.

Normally in unloading preforms from the injection molding machine by useof the unloading device and transferring them to the conveying device,the unloading device is rotated to put the preforms in an invertedorientation and is lowered in position in the height direction to bringthe preforms close to the supporting parts, and the preforms are droppedacross some height and thereby transferred to the respective supportingparts.

With the arrangement of the second aspect, since the slide table can beraised or lowered to set the height position of the supporting parts toan appropriate position, the transfer of the preforms from the unloadingdevice can be performed more smoothly and the degree of freedom of theconfiguration of the injection molding machine, unloading device, andconveying device can be increased.

Also, by combining the operation of the unloading device and therising/lowering operation of the slide table, the time required fortransferring the preforms can be shortened.

A third aspect of exemplary embodiments includes each supporting parthaving a head part, which is fitted into a preform from a mouth part andmaintains the orientation of the preform, and this head part beingarranged to be swingable in its orientation within a fixed range.

Though with regard to the arrangement of a supporting part, for examplea method of providing an indented part into which the mouth part of thepreform is fitted, a method of providing a protruding part that isfitted into the mouth part, etc., may be employed according to purpose,with the above-described arrangement of the third aspect, even if thereis a slight positional deviation and there is a slight tilt in theorientation of a preform when the preform is transferred from theunloading device to a supporting part, the head part can accommodate forthis deviation and tilt by tilting to enable smooth transfer to beachieved, the tolerance of the precision of the positioning of devicesto be widened, the device arrangement to be simplified, the timerequired for positional adjustments to be shortened, and thus theproduction speed to be improved.

Also, when a preform is transferred from a slide plate to the gripconveyer, the downstream part of the grip conveyer is raised and set inan inclined manner to pull up and remove the preform from a supportingpart, and this removal can be carried out smoothly by making the headpart swingable in orientation. Production problems can thus be preventedand the widening of the tolerance of the precision of the positioning ofdevices, simplification of the device arrangement, and improvement ofthe production speed are enabled for this reason as well.

A fourth aspect of exemplary embodiments includes the material and shapeof each grip and the spacing between grips that sandwich a preform fromboth sides being arranged to enable slipping between the preform and thegrips under a loaded state of a fixed range or more.

With the above-described arrangement of the fourth aspect, when in theconveying of preforms by the grip conveyor, the movement of the preformsis disabled for some reason and a load of a fixed range or more isgenerated, just the grip conveyor can be actuated without moving thepreforms to enable countermeasures against production problems to betaken readily.

A fifth aspect of exemplary embodiments includes each grip being made ofa short quadrilateral tube in shape, with the shape of the quadrilateralof the short quadrilateral tubular body being a parallelogram withwhich, with respect to a base end edge that is fixed to a chain of thegrip conveyor, a grip edge that opposes the base end edge and contacts apreform is shifted in parallel in the direction opposite the directionof progress of the chain.

With the above-described arrangement of the fifth aspect, when themovement of the preforms is disabled for some reason and a load of afixed range or more is generated, since the parallelogram shapes of thegrips collapse further in the direction opposite the direction ofprogress of the chain and flatten, the slipping between the grips andpreforms is made smoother.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall plan view showing an embodiment of this invention.

FIG. 2 is a plan view showing a state of progress of the conveying ofpreforms according to the embodiment shown in FIG. 1.

FIG. 3 is a side view showing a state of progress of the conveying ofpreforms according to the embodiment shown in FIG. 1.

FIG. 4 shows a (a) partial longitudinal sectional view and a (b) sideview of a preform supporting part of the embodiment shown in FIG. 1.

FIG. 5 is a plan view showing the principle parts of the grip conveyorof the embodiment shown in FIG. 1 in an enlarged manner.

FIG. 6 is an explanatory diagram showing an example of a prior-artpreform conveying device.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of this invention's conveying device shall now bedescribed with reference to FIGS. 1 through 5.

FIG. 1 is a plan view showing an embodiment of this invention'sconveying device and shows a state prior to the receiving of preforms Pfrom an unloading device 31 by conveying device.

As shown in FIG. 1, conveying device comprises a frame 2, a slide table3, which is slidably mounted on frame 2, six slide plates 4, disposed inparallel on slide table 3, a grip conveyor 21, etc., and a preformalignment part 1 is formed by the six slide plates 4.

Frame 2 is equipped with two Y-axis rails 6 y, which run parallel alonga Y-direction, and slide table 3 is set on Y-axis rails 6 y in a mannersuch that it is movable with its upper face being horizontal. Frame 2 isprovided with a Y-axis servo motor 7 y and slide table 3 is driven alongY-axis rails 6 y by Y-axis servo motor 7 y. Furthermore, the entirety ofslide table 3, including Y-axis servo motor 7 y, is supported from belowby a cylinder 8 and enabled to be raised or lowered suitably byactuation of cylinder 8.

Six X-axis rails 6 x are installed in parallel along an X-direction onslide table 3, and on each of the six X-axis rails 6 x is installed aslider 5 in a manner such that it is movable with its upper face beinghorizontal. When an X-axis rail 6 x is positioned above a conveying lineL, a slider 5 is moved along the X-axis rail 6 x by the driving of anX-axis servo motor 7 x installed on conveying line L. Furthermore, ontothis slider 5 is fixed a slide plate 4 having 16 supporting parts 11mounted on the upper face as shown in FIG. 1.

As shown in FIGS. 4( a) and (b), a supporting part 11 comprises a headpart 12, a fixed part 13, which is fixed to a slide plate 4, a shaft pin14, which is slidably mounted inside fixed part 13, a spring holdingpart 16, which is fixed to a lower part of shaft pin 14, a spring 15,which urges shaft pin 14 downwards via holding part 16, etc.

Fixed part 13 is fitted and fixed by screwing in a circular hole formedin slide plate 4 and has a hole in the center through which shaft pin 14passes. Head part 12 as a whole is formed to a shape that holds apreform P in an inverted orientation by being fitted in from an openingat a mouth part P1. Also, the lower end face of head part 12 is formedto a spherical shape that protrudes downwards. This head part 12 isscrewed onto and thereby assembled and fixed onto the upper end part ofshaft pin 14.

Since as mentioned above, shaft pin 14 is urged downwards by spring 15via spring holding part 16 and the lower end face of head part 12 isspherical, supporting part 11 is put in contact in a pressed stateagainst the upper end face of fixed part 13 and is allowed to undergo aswinging motion within a predetermined range.

In the mold (not shown) for injection molding of preforms P, 16 cavitiesare formed in the vertical direction and six such rows of cavities arealigned in the lateral direction, that is, a total of 96 cavities arealigned. Preforms P that have been injection molded are unloaded byunloading device 31 in the same state of alignment as this alignment ofcavities. The preforms P that have been unloaded by unloading device 31are transferred to the conveying device.

FIG. 1 shows a state in which the centers in the X-direction of therespective slide plates 4 (for convenience, the symbols <1> to <6> areattached to distinguish the respective slide plates 4) are aligned at aposition X1 and the central axis in the Y-direction of slide plates 4 ofthe first row (indicated by <1> here) are aligned at a position Yc inthe Y-direction of conveying line L of grip conveyor 21, which shall bedescribed later.

By aligning slide plates 4 at position X1 and position Yc as describedabove, supporting parts 11 are made to correspond to the alignment stateof unloading device 31.

FIG. 5 is a plan view showing the principle parts of grip conveyor 21 inan enlarged manner. Grip conveyor 21 has chains 23, revolvably woundbetween rotating bodies 24, disposed in an opposing manner at both sidesof conveying line L along the X-direction. Each chain 23 has rubbergrips 22 mounted in a continuous manner and conveys preforms P in thedirection of the arrow with the body parts P2 of preforms P beingsandwiched by grip parts 22.

Furthermore, conveying line L has its upstream end positioned abovepreform alignment part 1 and has its downstream part raised upwards andinclined (see FIGS. 1 and 3).

Also, as shown in FIG. 5, each grip 22 is formed to a shortquadrilateral tube with a parallelogram shape with which, with respectto a base end edge 25 that is fixed to chain 23, a grip edge 26 at theside that contacts a preform P is shifted in parallel in the directionopposite the direction of progress of chain 23. By making grips 22 be ofthis shape, even when preforms P become unmovable within conveying lineL, the parallelograms of grips 22 will flatten by deforming in thedirection opposite the direction of conveying of preforms P and enableslipping of preforms P and grips 22 so that grip conveyor 21 will notstop completely and measures for the occurrence of a problem can betaken readily.

The method by which preforms P are conveyed using conveying device shallnow be described using FIGS. 1, 2, and 3.

FIG. 3 shows states in which preforms P are transferred from unloadingdevice 31 to slide plates 4 and are transferred from slide plates 4 togrip conveyer 21.

First, normally upon unloading preforms P from the cavities of the moldof the injection molding machine, unloading device 31 is in the stateindicated as A. From this A state, rotation by 90° is performed to reachthe state indicated by B, in other words, the respective preforms P areput in inverted states, and preforms P are then lowered from a heightposition Z4 to a position Z3.

Meanwhile, Y-axis servo motor 7 y, etc., are actuated to put thepositions of slide table 3 and slide plates 4 in the X-Y plane in thestate shown in FIG. 1. Also with regard to the height direction, slidetable 3 is raised from a position Z1 to a position Z2 by means ofcylinder 8. Then upon slightly fitting head parts 12 of supporting parts11 in mouth parts P1 of preforms P, the respective preforms P aredropped across some height. The respective preforms P thus become fixedas they are in the inverted orientations onto the corresponding headparts 12.

Positions Z1 to Z4 are set to optimal values according to theconfiguration of the injection molding machine, unloading device 31, andconveying device, the times required for the respective processes, etc.The height across which preforms P are to be dropped onto supportingparts 11 is set to a value by which head parts 12 can be fitted withoutfail into mouth parts P1. Here, since head parts 12 are swingable inorientation, positioning errors can be compensated by the swingingactions and the process of fitting into mouth parts P1 can beaccomplished smoothly.

At unloading device 31, the operations of holding and dropping preformsP onto the supporting parts are performed.

Also, slide table 3 does not necessarily have to be raised from positionZ1 to position Z2 in general, and unloading device 31 may instead bearranged to be lowered to an appropriate position with respect to slidetable 3 positioned at position Z1 to transfer preforms P. However, in acase where the transfer speed of preforms P is to be increased asdescribed above or in a case where the dimensions of preforms P arechanged, etc., it is preferable to raise or lower the position of slidetable 3.

When preforms P have been fitted onto supporting parts 11, unloadingdevice 31 and slide table 3 return to the original height position Z4and position Z1, respectively. Then as shown in FIG. 1, the position inthe Y-direction of slide plate 4 of <1>becomes the position Yc onconveying line L of grip conveyor 21, and by X-axis servo motor 7 xbeing driven in this state, slider 5 moves in the direction of aposition X2 along X-axis rails 6 x. By the movement of slider 5, slideplate 4 is moved below grip conveyer 21, and the individual preforms Pare then transferred to grip conveyor 21.

In this process, since the movement speed of slide plate 4 in thedirection of position X2 and the conveying speed of grip conveyor 21 aremade equal and grip conveyer 21 is raised at its downstream side and putin an inclined state, mouth part P1 of each preform P becomes removedsmoothly from head part 12 of supporting part 11 in the transferprocess.

Also, even if the positioning deviates somewhat due to reasons ofmechanical dimensional precision and the inner peripheral face of amouth part P1 of a preform P contacts head part 12 somewhat, since headpart 12 is arranged to be swingable in orientation within a fixed range,such a deviation can be absorbed by the swinging of head part 12 and thetransfer can be accomplished smoothly.

Though with the above-described embodiment, a case where the movementspeed of slide plate 4 and the conveying speed of grip conveyor 21 areset to the same speed was described, there are also cases where thetransfer of preforms P can be achieved more smoothly by providing adifference in the speeds of the two components.

When the transfer of preforms P on slide plate 4 of <1> in theabove-described manner is completed, slide table 3 is moved by means ofY-axis servo motor 7 y and the same operations are repeated upon settingslide plate 4 of <2> at position Yc.

FIG. 2, is a plan view like FIG. 1 and shows a state in which slideplate 4 of <5> is set at position Yc and preforms P are transferred togrip conveyor 21. Preforms P on slide plates 4 of <1> to <6> are thustransferred successively to grip conveyor 21, thereby arranging thevertically and laterally aligned plurality of preforms P in single rowsand conveying them to the blow molding process or other subsequentprocess side.

When the transfer of preforms P on slide plate 4 of <6> is completed,the positions of slide table 3 and slide plates 4 are returned to thestate shown in FIG. 1 and preforms P, molded by the injection moldingmachine, are received from unloading device 31 again.

EFFECTS OF THE INVENTION

With the first aspect of various exemplary embodiments the preformconveying device of the invention, collision or friction of preformswith each other can be eliminated, and since the contact of parts of theconveying device with the outer surfaces of preforms can be restrictedto that of the gripping by rubber grips formed of a rubber-like, softmaterial, the problem of flawing of the preforms or the problem of thesoiling of the outer surfaces of preforms will not occur.

Also, since only the preforms are moved to the blow molding process orother subsequent process side and since movement to the subsequentprocess side, return to the conveying device, and realignment are thusmade unnecessary for the supporting parts, the conveying device can bemade simple in structure and handling.

With the second aspect of the invention, since the slide table can beset at an appropriate position by raising or lowering of the slidetable, the transfer of the preforms from the injection molding machineto the conveying device can be performed smoothly and productionproblems can be restrained.

Also, the degree of freedom of the configuration of the injectionmolding machine, unloading device, and preform conveying device can beincreased, and furthermore, by combining the operation of the unloadingdevice and the rising/lowering operation of the slide table, the timerequired for transferring the preforms can be shortened.

With the third aspect of the invention, since the head parts ofsupporting parts are made swingable, the transfer of preforms from thepreform unloading device to the supporting parts and the transfer ofpreforms from the supporting parts to the grip conveyor can beaccomplished more smoothly, thus enabling the prevention of productionproblems as well as the widening of the tolerance of the precision ofthe positioning of devices, simplification of the device arrangement,shortening of the time required for positional adjustments, andimprovement of the production speed.

With the fourth aspect of the invention, since the material and shape ofeach grip and the spacing between grips are arranged to enable slippingbetween the preform and the rubber grips under a loaded state of a fixedrange or more so that just the conveyor can be made movable when themovement of the preforms is disabled for some reason, countermeasuresagainst production problems can be taken readily.

With the fifth aspect of the invention, since grips with a parallelogramshape are flattened by collapsing in the direction opposite thedirection of conveying of the preforms, the slipping between the gripsand preforms can be made smooth without excess effort.

1. A preform conveying device, receiving, via an unloading device (31),preforms (P), which have been molded by an injection molding machinehaving a plurality of preform molding cavities aligned vertically andlaterally, and supplying said preforms (P) to a subsequent process sideupon alignment in single rows, said device comprising: a preformaligning part (1), having a slide table (3) installed on a frame (2) ina manner enabling sliding in a Y-direction that is a single horizontaldirection and having, on said slide table (3), slide plates (4), eachprovided with supporting parts (11) that respectively hold individualpreforms (P) in inverted states at alignment positions corresponding tothe alignment of the preforms (P) in a single vertical row of saidunloading device (31), said slide plates (4) being at least the same innumber as the number of vertical rows of said unloading device (31) andbeing aligned parallel to a horizontal X-direction, perpendicular to theY-direction, at intervals corresponding to the alignment of saidvertical rows in a manner enabling sliding individually in theX-direction; and a grip conveyor (21), having grips (22) formed of arubber-like soft material for holding said preforms (P) in a sandwichingmanner and having, in a state in which a conveying line (L) formedthereby is aligned in direction in the X-direction and inclined by theraising of a downstream part, an upstream end positioned above saidpreform alignment part (1); wherein each slide plate (4), upon beingsuccessively set by the sliding of said slide table (3) in theY-direction so that its Y-direction position matches the Y-directionposition of the conveying line (L) formed by said grip conveyor (21), isslid in the X-direction at substantially the same speed as the conveyingspeed of said grip conveyor (21) and moved below said grip conveyor (21)as the individual preforms (P) are transferred to the grip conveyor(21).
 2. The preform conveying device according to claim 1, wherein theslide table (3) is installed in a manner enabling rising and loweringwith respect to the frame (2).
 3. The preform conveying device accordingto claim 1, wherein each supporting part (11) has a head part (12),which is fitted into a preform (P) from a mouth part (P2) and maintainsthe orientation of said preform (P), said head part (12) being arrangedto be swingable in its orientation within a fixed range.
 4. The preformconveying device according to claim 1, wherein the material and shape ofeach grip (22) and the spacing between grips (22) that sandwich apreform (P) from both sides are arranged to enable slipping between saidpreform (P) and the grips (22) under a loaded state of a fixed range ormore.
 5. The preform conveying device according to claim 4, wherein eachgrip (22) is made a short quadrilateral tube in shape with the shape ofthe quadrilateral of the short quadrilateral tubular body being aparallelogram with which, with respect to a base end edge that is fixedto a chain (23) of the grip conveyor (21), a grip edge (26) that opposessaid base end edge (25) and contacts a preform is shifted in parallel inthe direction opposite the direction of progress of the chain (23). 6.The preform conveying device according to claim 2, wherein eachsupporting part (11) has a head part (12), which is fitted into apreform (P) from a mouth part (P2) and maintains the orientation of saidpreform (P), said head part (12) being arranged to be swingable in itsorientation within a fixed range.
 7. The preform conveying deviceaccording to claim 2, wherein the material and shape of each grip (22)and the spacing between grips (22) that sandwich a preform (P) from bothsides are arranged to enable slipping between said preform (P) and thegrips (22) under a loaded state of a fixed range or more.
 8. The preformconveying device according to claim 3, wherein the material and shape ofeach grip (22) and the spacing between grips (22) that sandwich apreform (P) from both sides are arranged to enable slipping between saidpreform (P) and the grips (22) under a loaded state of a fixed range ormore.